Ok, sorry, I must have missed the end of your post...
In any case, the PMDG 737 is not a special case, the only airplanes in the current version of the GSX internal database that we added a special handling of the parking brakes which includes testing the Wheel chocks are the Aerosoft Airbus series.
Every other airplane, including the PMDG 737, is only tested against the standard FSX parking brakes variable.
This means, when it happened, it wasn't set by the PMDG itself, and it was probably re-set correctly when acting on the Wheel chocks for some reason.